One of the targets in the development of telecommunication networks is to provide the user with an IP service, i.e. access to the Internet through an access network. The basic IP concept does not support the mobility of the user, and therefore, a mobile IP protocol has been introduced by the Internet Engineering Task Force (IETF) in order to enhance the mobility in the Internet. Mobile IP enables routing of IP datagrams to mobile nodes independently of the point of attachment in the sub-network. In the basic IP, the IP addresses are assigned to network interfaces in dependence on their physical location, which prevents the user (the mobile node) from keeping its address while moving over different Internet sub-nets, i.e. while changing the physical interface.
Mobile node (MN) refers to an IP node that is capable of changing its point of attachment from one network or sub-network to another. A mobile node may change its location without changing its IP address; it may continue to communicate with other Internet nodes at any location using its (permanent) IP address. When a mobile node visits a foreign network, a care-of-address (C/O-address) is temporarily assigned to the mobile node. The IP datagrams addressed to the mobile node are forwarded to this care-of-address.
A critical issue for the success of next generation mobile networks is the ability of seamless IP-layer mobility. Seamless mobility is the ability to hand a mobile node (MN) over from one (old) access router (AR) to another (new) access router with minimal service disruption. An access router refers to an access network router residing on the edge of an access network and connected to one or more access points (AP), i.e. base stations. The access points may be of different technology. An access router offers IP connectivity to mobile nodes, acting as a default router to the mobile nodes it is currently serving.
Discovering neighboring access routers within the access router's proximity is considered an important part of the ability of providing seamless handovers in IP based mobile networks. Mechanisms for realizing protocols to discover neighboring access routers and their capabilities to facilitate seamless handovers have been proposed in e.g. [1] D. Trossen et al., “A Dynamic Protocol for Candidate Access Router Discovery”, Work In Progress, IETF Internet Draft, October 2002, and D. Funato et al., “Geographically Adjacent Access Router Discovery Protocol”, Work In Progress, IETF Internet Draft, December 2002.
The selection of the target access router (TAR), i.e. the access router to which the mobile node is eventually handed over, is not defined in the context of candidate access router (CAR) discovery, albeit it is the subsequent action to any CAR discovery solution. However, this step is not within the scope of CAR discovery, as outlined in D. Trossen et al., “Issues in Candidate Access Router Discovery for Seamless IP-level Handoffs”, Work In Progress, IETF Internet Draft, October 2002.
According to prior art solutions, candidate access router discovery protocols are realized either in the access routers or in the mobile nodes or in both. A possible problem relating to prior art solutions is that access routers may belong to different network operators and, thus, operators have to reveal various confidential information, e.g. capability information, to other operators. Furthermore, when the logic controlling the candidate access router discovery has to be updated, it must be performed in each access router separately. On the other hand, if the candidate access router discovery protocols are realized solely in the mobile nodes, this might lead to an excessive data exchange over the wireless link.